The present disclosure relates to an apparatus for forming various circuits to be connected to a capacitive element and using a proper capacitive element value to obtain an optimal capacitive reactance value required in a resonance.
An antenna is a device receiving an RF signal in the air inside a terminal or transmitting a signal inside the terminal outwardly, which is an essential element of a wireless device for communication with the outside.
FIG. 1 is a configuration view illustrating an antenna 10 according to related art. Referring to FIG. 1, the antenna 10 includes a feeding part 11 and radiating bodies 12a and 12b. In the antenna 10, the feeding part 11 is connected to the radiating bodies 12a and 12b in series and a signal provided by the feeding part 11 is transmitted to the outside via the radiating bodies 12a and 12b. 
In this case, the radiating bodies 12a and 12b may be grounds (not shown) of a wireless communication device or may be additional radiating bodies. On the other hand, one 12a may be an additional radiating body and another 12b may employ a ground body as a radiating body.
In case of the antenna 10 of FIG. 1, since an electric signal is directly provided from the feeding part 11 to the radiating bodies 12a and 12b by only using an electric method without an additional feeding structure, a performance thereof is lower than that of an antenna including a feeding structure.
FIG. 2 is a view illustrating an antenna 20 including a feeding structure according to related art.
Referring to FIG. 2, the antenna 20 includes a feeding part 21, radiating bodies 22a and 22b, and a conductive line 24 for forming a feeding loop 25.
In case of the antenna 20 of FIG. 2, since the feeding loop 25 is formed by using the conductive line 24, it is possible to perform feeding by magnetic coupling in addition to electric feeding, thereby providing more improved performance than the antenna 10 of FIG. 1, which does not include the feeding loop 25. However, though the antenna 20 includes the feeding loop 25, a performance thereof is decreased in a high frequency area. A detailed description thereof is as follows.
When an RF current provided from the feeding part 21 flows through the feeding loop 25, there is generated an equivalent magnetic current Im. The equivalent magnetic current Im is expressed as follows.Iml=jωμSI(ω)  Equation (1)
In Equation 1, j indicates an equivalent magnetic current having a length, ω indicates an angular frequency, μ indicates permeability, S indicates an area of a feeding loop, and I(ω) indicates an RF currrent provided from a feeding part.
The equivalent magnetic current Im generated in the feeding loop 25 may be considered as a magnetic flux generated in the feeding loop 25, and a relation between the magnetic flux generated in the feeding loop 25 and the equivalent magnetic current Im is expressed as follows.Im=−jωψ  Equation (2)
In Equation 2, ψ indicates a total sum of the magnetic flux generated in the feeding loop 25.
On the other hand, the total sum of the magnetic flux generated in the feeding loop 25 may be expressed as follows.
                                                        ψ              =                            ⁢                                                ∫                                                            B                      →                                        ·                                          ⅆ                                              s                        →                                                                                            ≈                                  B                  ·                  s                                                                                                        =                            ⁢                              L                ·                I                                                                                        =                            ⁢                              L                ⁢                                  V                                      R                    +                                          j                      ⁢                                                                                          ⁢                      ω                      ⁢                                                                                          ⁢                      L                                                                                                                                              ∝                            ⁢                              1                ω                                                                        Equation        ⁢                                  ⁢                  (          3          )                    
According to Equation 3, it can be known that a total amount of the magnetic flux generated in the feeding loop 25 is reduced as a frequency of the RF current provided from the feeding part 21 increases.
That is, the reduction of the total amount of the magnetic flux generated in the feeding loop 25 means a reduction of the equivalent magnetic current Im. Accordingly, since the equivalent magnetic current Im is reduced at a high frequency and it is impossible to efficiently feed the RF signal to the radiating bodies 22a and 22b, the performance of the antenna 20 of FIG. 2 is decreased at the high frequency and a band thereof may become narrower.
On the other hand, in an antenna structure, it is standardized that capacitance value (0.3 to 1.5 pF) that is a low capacitive element is used in 1800 MHz or more and a high capacitance value (6 to 9 pF) is used in 960 MHz or less.
In this case, a product standardized as a low capacitance of 2 pF or less exists as a 0.1 pF unit and a product standardized as a high capacitance of 6 pF or more exists as a 1 pF unit.
However, since antennas are more sensitive than a standardized tolerance of a capacitance, a capacitance value that is not standardized is needed when forming a resonance at a desired frequency.